1. Field of the Invention
This invention relates to a ratchet driving mechanism, and more particularly to a ratchet driving mechanism that includes two sets of pawls.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a ratchet driving mechanism 1 disclosed in U.S. Pat. No. 6,047,802 by the applicant is used to interconnect a screwdriver 20 and a grip 30, and includes an anchoring unit 11, a switching unit 12, and a ratchet unit 13.
The anchoring unit 11 is connected to the grip 30, and includes a main body 111, which has opposite first and second end surfaces 112, 113, and an annular outer surface 114 interconnecting the first and second end surfaces 112, 113. The first end surface 112 is formed with two open-ended slots 115 parallel to each other.
The switching unit 12 includes an adjusting ring 121 sleeved rotatably on the main body 111 and having an inner surface formed with two retaining grooves 122.
The ratchet unit 13 includes a ratchet wheel 131 connected to the screwdriver bit 20 and sleeved rotatably on the main body 111, two resilient members 132 disposed respectively within the slots 115, and first and second pawls 133, 134 disposed respectively within the slots 115 and biased respectively by the resilient members 132 to project respectively from the slots 115. The ratchet wheel 131 has a ratchet-toothed annular inner surface 135.
The adjusting ring 121 is operable to rotate among an anchoring position shown in FIG. 2, a first-direction position shown in FIG. 3, and a second-direction position shown in FIG. 4.
When the adjusting ring 121 is disposed in the anchoring position, each of the first and second pawls 133, 134 engages a respective one of the retaining grooves 122 and the ratchet-toothed annular inner surface 135. As such, rotation of the ratchet wheel 131 on the main body 111 is prevented.
When the adjusting ring 121 is disposed in the first-direction position, only the second pawl 134 engages the corresponding retaining groove 122 and the ratchet-toothed annular inner surface 135 so as to allow for rotation of the ratchet wheel 131 on the main body 111 in only a first rotational direction (A).
When the adjusting ring 121 is disposed in the second-direction position, only the first pawl 133 engages the corresponding retaining groove 122 and the ratchet-toothed annular inner surface 135 so as to allow for rotation of the ratchet wheel 131 on the main body 111 in only a second rotational direction (B) that is opposite to the first rotational direction (A).
When the adjusting ring 121 is disposed in the first-direction or second-direction position, due to engagement between the ratchet-toothed annular inner surface 135 and only a single pawl 133, 134, an insufficient driving surface is obtained such that only a minimal torque may be accommodated. As a result, the ratchet-toothed annular inner surface 135 as well as the first and second pawls 133, 134 easily experience wearing during operation, thereby reducing the service life of the ratchet driving mechanism.